The present invention relates to a method and to an apparatus for making shoe lasts and/or components for shoes.
A shoe last is a block or form shaped like a human foot used in manufacturing shoes and also in repairing shoes. In the manufacture of shoes, a model last is produced for each particular shoe last style, and then a plurality of graded lasts are produced according to the different lengths and widths to be made available for the respective shoe style.
The grading procedure is usually not a straightforward one wherein all dimensions are proportionately increased with the increase in size; rather, to avoid distortions, and also to minimize the initial tooling costs (e.g., moulds) required to manufacture the shoe components, many dimensions are not increased, or are disproportionately increased, for a plurality of grades. For example, "bottom-holding", "heel-height holding", "toe-spring holding", and "toe-thickness holding" techniques are frequently used in order to maintain certain dimensions for a plurality of sizes, or to change the dimensions in a non-linear manner with respect to the different sizes.
An important factor of the respective style influencing the grading procedure is the feather line of the model last, namely the juncture line of the last bottom with the last sides. The feather line determines the outer configuration of the last bottom and is frequently involved in these "holding" techniques.
Generally speaking, producing graded lasts from a model last not only requires a high degree of expertise and experience, but also is very expensive and time- consuming. According to present techniques, a model last for each style is first produced by an artisan model-maker, and then the graded lasts, corresponding to the different sizes of the same basic style, are usually prepared by a pantograph machine, in which the different sizes are produced by adjusting the arms of the pantograph. However, this method produces considerable distortions which are cumulative; that is, a distortion from one size to the next may not be too significant, but they become very significant when they are magnified by differences in three or four sizes. These distortions therefore require considerable "retouching" by the last maker; moreover, they limit the variations possible as a practical matter in the different grades.
The components (e.g., the flat leather, plastic, fabric blanks for making the sides, soles, heels, etc.) used in manufacturing the shoe are uusually indicated by style-lines marked on the model last. These style-lines also indicate the stitching lines of the various components used in the manufacture of the shoes, and thereby the configurations of such components. Techniques are known for converting the three-dimensional configuration of a shoe component, as determined by three or more style-lines on the shoe last, to a two-dimensional configuration for manufacturing the respective components. However, determining the three-dimensional configuration of the components in all the grades (sizes) of the respective shoe style is also very time-consuming and requires a high degree of expertise and experience.